The invention relates to a case seal for transversely-divided crankcases.
Many engines have transversely-divided crankcases. Transversely-divided crankcases can be found in particular on small two-cycle engines, such as are used for motor-driven hand tools.
Such crankcases have an upper crankcase element, which is associated with the cylinder, and a lower crankcase shell. For assembly, the piston, connecting rod and the crankshaft, together with bearings and shaft seals, are inserted into the upper crankcase element, and thereafter the crankcase is closed by means of the lower crankcase shell.
Both crankcase halves have bearing seats, into which the bearings of the crankshaft are inserted. Roller bearings, which must be securely maintained in the bearing seats, are mostly used in connection with small two-cycle engines. It must be assured that the bearings cannot become twisted in the bearing seats and are arranged, exactly placed in respect to the cylinder track, in the crankcase half assigned to the cylinder.
Furthermore, the separating line between the two case halves must be sealed. Sealing is important, in particular in the case of two-cycle engines, so that the crankcase pressures required for the gas exchange can be assured. When assembling the crankcase it is therefore necessary to make sure at the same time that the bearings are held in place with the required force without being firmly clamped, that the bearings are correctly positioned, and that the required sealing effect at the crankcase separating line is achieved at the same time.
Liquid sealing material is mostly used for sealing the crankcase separating line. With the crankcase closed, the bearing seats must exert a defined force on the bearing for fixing them in place, wherein it is necessary at the same time to close the crankcase separating line in such an exact manner-that a sufficient sealing effect is achieved with the liquid sealing material. It is also possible to employ a thin paper seal alternatively with the liquid sealing material. However, the size of the seal must be matched to the size of the separating line, so that the bearings are sufficiently fixed in place.
Components and surfaces exactly matched to each other, as well as careful assembly, are prerequisites for the trouble-free operation of the engine. Leaks in the transition area between the housing gap and the bearing seats often occur, in particular, with the conventional solution of the problem. Further than that, positional inaccuracies of the bearing seats lead to damage to the crankshaft. Bearing damage often also occurs as a result of inaccurate bearing seats because of twisting of the bearings in the course of screwing the crankcase together.
It is therefore the object of the invention to make a case seal available, which provides a dependable seal between the two case halves, in particular in the transition area between the housing gap and the bearing seats, and which at the same time makes possible a simple and dependable seating of the crankshaft bearings in the bearing seats in the case, as well as a sufficient positioning of the crankshaft in respect to the cylinder track. It is intended in particular that for achieving a cost-effective production, machining of the bearing seats should be omitted and a rapid assembly be made possible.
To attain this object, a case seal for transversely-divided crankcases composed of an upper crankcase element and a lower crankcase shell is proposed, wherein both case halves have bearing seats for seating a shaft, which is distinguished in that the case seal is designed as a one-piece resilient molded element, which can be placed on one crankcase half along the sealing faces and the bearing seats.
Such a case seal is produced as a molded element, which is placed on the sealing faces and the faces of the bearing seats of one crankcase half.
The seal can preferably be embodied in such a way that it also runs along the seats of the shaft seal rings of a crankshaft half. It can be shaped in such a way that it can be placed either on the lower crankcase element or on the upper crankcase element.
The crankcase bearings can also be inserted into non-machined bearing seats in the crankcase. The crankcase bearings are pressed with a defined force into their bearing seats in the oppositely located crankcase half. Turning of the crankcase bearings along with the shaft is reduced, production tolerances in the area of the machined or non-machined sealing faces, the bearing seats and the shaft seal rings, are compensated by the resilient seal.
It is achieved at the same time that a dependable sealing effect is assured along the crankcase separating line.
The radial seal of the shaft is provided in the customary manner by means of a shaft seal ring. Thus, the case seal performs a sealing function in the area of the crankcase separating line, while in the area of the bearing seats it provides a dependable seating for the shaft bearings, or respectively for the crankshaft.
If the seal also extends along the shaft seal seats, it can compensate production tolerances here and improve the sealing effect.
A rubber material which must be gasoline- and oil-resistant is preferably selected for the resilient molded element.
In a further development of the invention the crankshaft half on which the seal is intended to be placed is provided with a groove in the area of the crankshaft separating line, into which the molded sealing element can be at least partially inserted. In the course of fastening the lower crankshaft shell on the upper crankshaft element, the seal is squeezed into the groove and a dependable sealing effect is assured.
Another further development of the invention provides that the bearing seats, the shaft seal ring seats, or both the bearing seat as well as the shaft seal seats, of the second crankshaft half, which is not provided with a seal, are at least partially rubber-coated. By means of this it is achieved that the bearings are additionally secured against twisting, and production tolerances are compensated. The sealing effect of the shaft seal rings is being improved.
For improving the seating of the crankshaft bearings in the bearing seats, as well as the sealing of the crankcase, the seal can additionally consist of a second resilient molded element, which can be placed into the bearing seat and/or the shaft seal ring seat of the second crankcase half, or can additionally be placed along the sealing face of the second crankcase half. The second sealing element can also correspond in its shape to the first sealing element or, with an appropriately shaped crankcase, can be outwardly identical with the first element. This helps to lower the production costs and to prevent assembly errors.
The crankshaft bearings are then completely enclosed in resilient material, which fixes them in place in the bearing seats by means of a defined pressure, positions them and protects them from twisting, and compensates tolerances as well.
The same as the first element, the second element of the seal can be made of rubber. It can also be connected in one piece with the first element.
The advantage of the case seal in accordance with the invention is that elaborate machining of the bearing seats in the crankcase halves can be avoided. The production tolerances are compensated by the resilient molded elements. The seal is squeezed to a defined extent by the predetermined defined spacing between the crankcase halves, and at the same time the crankshaft bearings are held in place in the seats by a defined pre-stress.
Moreover, the use of liquid sealing material is no longer required. An efficient, cost-saving, clean manufacture is made possible. The seal can be prefabricated in one piece. Assembly errors and inaccuracies, which later lead to leaks in the engine, are impossible.